In-flight refuelling systems of a known type envisage the transfer of fuel between a tanker aircraft and a receiver aircraft by means of a hose passing through a rigid pipe (known as “boom”) and a telescopic line. The boom is fixed to a rear portion of the fuselage of the tanker aircraft through a semi-rigid connection, which enables a certain degree of freedom of movement. It is evident that the receiver aircraft, in order to carry out successfully the operation of in-flight refuelling, must first of all carry out a correct approach to the tanker aircraft, keeping a distance not greater than the distance that can be covered by the boom and the telescopic line, and then maintain a position and a speed as conformable as possible to that of the tanker aircraft.
A different refuelling method envisages instead the use of a hose, provided, on a terminal portion thereof, with a drogue, configured for connecting up to an inlet mouth of the refuelling system of the receiver aircraft. The receiver aircraft must execute minimal movements such as to reach the drogue of the hose and remain in a fixed position with respect to the tanker aircraft.
The operation of approach of the receiver aircraft to the area envisaged for refuelling (known as “rendez-vous area”) and of initial positioning with respect to the tanker aircraft is currently executed by the pilot of the receiver aircraft. For experimental purposes, during the most critical operations of fine alignment (for example, engagement of the hose with the fuel-receiving line of the receiver aircraft) tests have been conducted, in which the pilot of the receiver aircraft is supported in the correct positioning by alignment systems of an optical type, in particular devices working in the visible or infrared devices, which issue an optical signal detected by appropriate optical detectors set on the receiver aircraft, in particular in the proximity of the fuel-receiving line. However, said alignment systems, used only in the terminal step of engagement with the fuel-receiving line, envisage an active intervention on the part of the pilot of the receiver aircraft in maintaining the position of the receiver aircraft stable with respect to that of the tanker aircraft during the refuelling procedure.
A solution of a known type to this problem is described in the U.S. Pat. No. 6,669,145. In detail, this solution envisages setting on the tanker aircraft and/or on the drogue fixed to the boom a plurality of reflectors, configured for operating as polarization filters. The receiver aircraft has, instead, available a source of radiation (for example, a LED or a laser) and a detector of radiation (for example, a photodiode).
In the final step of approach between the receiver aircraft and the tanker aircraft, the receiver aircraft issues, by means of the source of radiation, an incident radiation that propagates in the direction of the tanker aircraft and/or of the drogue. The reflectors set on the tanker aircraft and/or on the drogue reflect the incident radiation, each generating a reflected radiation of its own (characterized by a polarization of its own), which is detected by the detector of radiation set on the receiver aircraft. By analysing the reflected radiation, and in particular the polarization of the signal received, the receiver aircraft is able to know its own position with respect to each reflector, and, consequently, with respect to the tanker aircraft and/or the boom.
The system described in U.S. Pat. No. 6,669,145 presents the disadvantage of entailing considerable modifications, including structural ones, to the tanker aircraft and to the drogue of the boom. This involves a high cost for updating existing tanker aircraft, and an increase in the production costs of tanker aircraft built according to the teaching of the document U.S. Pat. No. 6,669,145. Furthermore, according to said system, a receiver aircraft that requires in-flight refuelling, could complete successfully the steps of refuelling by interfacing only with a tanker aircraft built according to the teaching of the document U.S. Pat. No. 6,669,145, and not with a generic tanker aircraft.
A further solution of a known type for carrying out automatic in-flight refuelling is described in US 2008/0265097. The method described in US 2008/0265097 regards control of the flight of the tanker aircraft and control of orientation of the boom. In this case, in fact, the tanker aircraft is provided with an inertial measurement unit (IMU), a GPS device, and a processor, configured for calculating a current state of inertial navigation of the tanker aircraft compensating possible errors (for example, due to phenomena of electronic noise of the IMU and GPS location errors). The tanker aircraft can moreover comprise electro-optical sensors, for acquiring images of the boom and/or of the receiver aircraft during the final step of approach for refuelling.
Finally, the patent No. GB 2 438 218 describes a method and a system for enabling relative flight of two aircraft, in particular a tanker aircraft and a receiver aircraft that is to be refuelled. The correct position of flight of the receiver aircraft is maintained by comparing position data obtained via a GPS receiver set both on the tanker aircraft and on the receiver aircraft. The GPS measurements are integrated with further measurements obtained by means of acceleration sensors and angular-velocity sensors, set both on board the tanker aircraft and on board the receiver aircraft. This system, however, does not guarantee a high degree of precision (at least at the centimeter level) during the final step of approach and contact between the boom and the receiver aircraft (last 10 m).